Breakaway support post for highway guardrail end treatments

Abstract

A breakaway support post ( 18, 210 ) is provided for a highway guardrail system ( 10 ) to enhance the safety of a vehicle impacting with either the rail face of the associated guardrail ( 16 ) or one end of the guardrail facing oncoming traffic. The breakaway support post may have upper and lower portions ( 26, 28 ) with a releasable coupling assembly ( 29, 211 ) disposed therebetween to maintain the upper and lower portions generally aligned with each other prior to the impact of a vehicle with one end of the associated guardrail. The breakaway support post may also have releasable coupling assembly ( 301 ) disposed between the upper and lower portions and a cable ( 303 ). The releasable coupling assembly may allow the upper portion to separate from the lower portion. The cable may be released by the support post during separation of the upper and lower portions. The coupling assembly preferably provides sufficient support during a rail face impact to direct an impacting vehicle back onto the associated roadway.

What is claimed is:  
     
       1. A breakaway support post for mounting a guardrail thereon as part of a highway guardrail system, comprising: 
       an elongated body having an upper portion including a first upper end and a first lower end, and a lower portion including a second upper end and a second lower end, the second lower end having a configuration for installation adjacent to a roadway, and the first lower end having a first substantially vertical surface thereon and the second upper end having a second substantially vertical surface thereon;  
       a first means for attaching a guardrail to the elongated body adjacent to the first upper end;  
       a second means for rotatably coupling the upper and the lower portions and for releasably securing the upper portion of the elongated body generally aligned with the lower portion of the elongated body, wherein the breakaway support post is for resisting a rail face impact with a guardrail is attached to the support post and wherein an impact with one end of a guardrail system incorporating the support post will tend to rotate the upper portion of the elongated body relative to the lower portion of the elongated body; wherein the second means includes a first plate having a first opening and a second opening therethrough, and a third substantially vertical surface thereon, a portion of the third substantially vertical surface being disposed against a portion of the first substantially vertical surface, and the first plate being secured to the first lower end by a weld;  
       a second plate having a third opening and a fourth opening therethrough, and a fourth substantially vertical surface thereon, a portion of the fourth substantially vertical surface being disposed against a portion of the second substantially vertical surface, the second plate being secured to the second upper end by a weld, the second plate being disposed adjacent to the first plate so that the first opening is aligned with the third opening, and the second opening is aligned with the fourth opening;  
       a pivot pin portion extending through the first and the third openings, the upper portion of the elongated body being rotatable about the pivot pin portion relative to the lower portion of the elongated body;  
       a shear pin having a shear pin portion extending through the second and the fourth openings, the shear pin portion being adapted to shear in response to a force to allow pivotal movement of the upper portion relative to the lower portion around the pivot pin portion, the pivot pin portion and the shear pin portion extending in a strong direction approximately perpendicular to the plates, wherein the support post exhibits a high mechanical strength in the strong direction, there being a weak direction generally perpendicular to the strong direction, wherein the support post exhibits a low mechanical strength in the weak direction; and  
       the first and second plates each have a first edge and a second edge, the first edge facing generally toward the weak direction, and the second edge facing generally away from the weak direction, wherein the first plate further includes a chamfer disposed between a bottom edge thereof and a lower portion of the second edge thereof, and wherein the second plate further includes a chamfer disposed between a top edge thereof and an upper portion of the second edge thereof, the chamfers being positioned so that the first plate does not engage the lower portion and the second plate does not engage the upper portion when the upper portion of the elongated body rotates relative to the lower portion of the elongated body.  
     
     
       2. A breakaway support post for mounting a guardrail thereon as part of a highway guardrail system, comprising: 
       an elongated body having an upper portion including a first upper end and a first lower end, and a lower portion including a second upper end and a second lower end, the second lower end having a configuration for installation adjacent to a roadway, and the first lower end having a first substantially vertical surface thereon and the second upper end having a second substantially vertical surface thereon;  
       a first means for attaching a guardrail to the elongated body adjacent to the first upper end;  
       a second means for rotatably coupling the upper and the lower portions and for releasably securing the upper portion of the elongated body generally aligned with the lower portion of the elongated body, wherein the breakaway support post is for resisting a rail face impact when the guardrail is attached to the support post and wherein an impact with one end of a guardrail system incorporating the support post will tend to rotate the upper portion of the elongated body relative to the lower portion of the elongated body, wherein the second means includes:  
       a first plate having a first opening and a second opening therethrough, and a third substantially vertical surface thereon, a portion of the third substantially vertical surface being disposed against a portion of the first substantially vertical surface, and the first plate being secured to the first lower end by a weld;  
       a second plate having a third opening and a fourth opening therethrough, and a fourth substantially vertical surface thereon, a portion of the fourth substantially vertical surface being disposed against a portion of the second substantially vertical surface, the second plate being secured to the second upper end by a weld, the second plate being disposed adjacent to the first plate so that the first opening is aligned with the third opening, and the second opening is aligned with the fourth opening;  
       a pivot pin portion extending through the first and the third openings, the upper portion of the elongated body being rotatable about the pivot pin portion relative to the lower portion of the elongated body;  
       a shear pin having a shear pin portion extending through the second and the fourth openings, the shear pin portion being adapted to shear in response to a force to allow pivotal movement of the upper portion relative to the lower portion around the pivot pin portion, the pivot pin portion and the shear pin portion extending in a strong direction approximately perpendicular to the plates, wherein the support post exhibits a high mechanical strength in the strong direction, there being a weak direction generally perpendicular to the strong direction, wherein the support post exhibits a low mechanical strength in the weak direction;  
       a fifth substantially vertical surface on a side of the upper portion opposite the side having the first substantially vertical surface;  
       a sixth substantially vertical surface on a side of the lower portion opposite the side having the second substantially vertical surface;  
       a third plate having fifth and sixth openings therethrough, and a seventh substantially vertical surface thereon, a portion of the seventh substantially vertical surface being disposed against the fifth substantially vertical surface, and the third plate being secured to the first lower end by a weld;  
       a fourth plate having seventh and eighth openings therethrough, and an eighth substantially vertical surface thereon, a portion of the eighth substantially vertical surface being disposed against the sixth substantially vertical surface, the fourth plate being secured to the second upper end by a weld, the fourth plate being disposed against the third plate, so that the fifth opening is aligned with the seventh opening and the sixth opening is aligned with the eighth opening, and the pivot pin portion further extending through the fifth and seventh openings in the strong direction;  
       a further shear pin portion extending through the sixth and the eighth openings in the strong direction, the further shear pin portion being adapted to shear in response to a force to allow pivotal movement of the upper portion relative to the lower portion around the pivot pin portion; and  
       the third and fourth plates each have a first edge and a second edge, the first edge facing generally toward the weak direction, and the second edge facing generally away from the weak direction, wherein the third plate further includes a chamfer disposed between a bottom edge thereof and a lower portion of the second edge thereof, and wherein the fourth plate further includes a chamfer disposed between a top edge thereof and an upper portion of the second edge thereof, the chamfers being positioned so that the third plate does not engage the lower portion and the fourth plate does not engage the upper portion when the upper portion of the elongated body rotates relative to the lower portion of the elongated body free of engagement between the fourth and third plates and the upper and lower portions, respectively.  
     
     
       3. A breakaway support post for mounting a guardrail thereon as part of a highway guardrail system, comprising: 
       an elongated body having an upper portion and a lower portion, the upper portion of the elongated body having a first end, the lower portion of the elongated body having a second end which may be installed adjacent to a roadway;  
       a first means for attaching a guardrail adjacent to the first end of the upper portion; and  
       a second means for rotatably coupling the upper and the lower portions and for releasably securing the upper portion of the elongated body generally aligned with the lower portion of the elongated body, wherein the breakaway support post is for resisting a rail face impact when the guardrail is attached, and wherein an impact with one end of the guardrail will tend to rotate the upper portion of the elongated body relative to the lower portion of the elongated body, wherein the second means includes:  
       a first plate coupled to the upper portion, the first plate having a first opening and a second opening therethrough;  
       a second plate coupled to the lower portion, the second plate having a third opening and a fourth opening therethrough, a portion of the first plate being disposed adjacent to a portion of the second plate so that the first and the third openings are aligned and the second and fourth openings are aligned;  
       a pivot bolt extending through the first and the third openings;  
       a shear bolt extending through the second and the fourth openings and being adapted to shear in response to a force to allow pivotal movement of the upper portion relative to the lower portion around the pivot bolt;  
       the shear bolt having a diameter less than the diameter of the pivot bolt;  
       the pivot bolt and the shear bolt extending in a strong direction approximately perpendicular to the plates, wherein the support post exhibits a high mechanical strength in the strong direction;  
       the support post having a weak direction generally perpendicular to the strong direction, wherein the support post exhibits a low mechanical strength in the weak direction;  
       a third plate coupled to the upper portion on a side opposite the first plate, the third plate having a fifth opening and a sixth opening therethrough;  
       a fourth plate coupled to the lower portion on a side opposite the second plate, the fourth plate having a seventh opening and an eighth opening therethrough, a portion of the third plate being disposed adjacent to a portion of the fourth plate so that the fifth and the seventh openings are aligned and the sixth and the eighth openings are aligned, and the pivot bolt further extending through the fifth and the seventh openings in the strong direction;  
       a further shear bolt extending through the sixth and the eighth openings in the strong direction, the shear bolts being co-axial with each other, the further shear bolt having a head at one end, and threads at an opposite end and including a further nut, the further nut engaging the threads of the further shear bolt, the further shear bolt having a diameter less than the diameter of the pivot bolt, and the further shear bolt being adapted to shear in response to a force to allow pivotal movement of the upper portion relative to the lower portion around the pivot bolt;  
       the shear bolt and the pivot bolt are generally vertically aligned with each other and wherein the first and the second plates each have a first edge facing toward the weak direction and a second edge facing away from the weak direction, the pivot bolt being disposed closer to the second edge of the plates than to the first edge thereof, and wherein the shear bolts are disposed closer to the first edge than to the second edge thereof; and  
       a first chamfer disposed between a bottom edge and a lower portion of the second edge of the first plate, and a second chamfer disposed between a top edge and an upper portion of the second edge of the second plate, the chamfers being positioned so that the first plate does not engage the lower portion and the second plate does not engage the upper portion when the upper portion of the elongated body rotates relative to the lower portion of the elongated body.